JP7463101B2 - glue - Google Patents

Description

The present invention relates to an adhesive that can exhibit surface tackiness to improve temporary adhesion, and can further exhibit excellent adhesive strength by enhancing adhesion even after temporary adhesion, has excellent transparency, and is particularly capable of suppressing brightness degradation when used to bond optical films.

Traditionally, adhesives containing a large amount of solvent have been used to bond plastic films and other materials in order to ensure a uniform amount of adhesive is applied. However, such adhesives release a large amount of solvent when dried, causing problems with toxicity, work safety, and environmental pollution.

For this reason, solvent-free adhesives that do not use solvents are attracting attention. Active energy ray-curable adhesives that cure with active energy rays such as ultraviolet rays and electron beams are widely used as such solvent-free adhesives. In particular, active energy ray-curable adhesives are widely used for bonding optical films used in liquid crystal displays and organic EL displays.

Furthermore, in recent years, in order to reduce cure shrinkage, improve yields, and fix extremely small areas, a two-stage curing system has been attracting attention in which an active energy ray-curable adhesive is applied, temporarily fixed by irradiating a small amount of active energy rays, and then further irradiated with active energy rays for full curing. In such two-stage curing, it is required that the adhesion is enhanced by irradiating active energy rays after the first temporary fixation, and that the resin component in the adhesive does not deform significantly when the adhesive is applied, when the first temporary fixation is performed, and when it is fully cured.

As an active energy ray curable adhesive used for bonding optical films, for example, Patent Document 1 describes an adhesive containing a radical polymerizable compound having an active methylene group and a radical polymerization initiator having a hydrogen abstracting action. However, although the adhesive described in Patent Document 1 has adhesive strength to a polarizing plate, when used for bonding other optical films, there are problems in that the adhesive strength is insufficient or the adhesion is not enhanced during two-stage curing, and sufficient adhesiveness cannot be exhibited.
In addition, Patent Document 2 describes an adhesive containing a pressure-sensitive adhesive containing a (meth)acrylic polymer containing an aromatic ring-containing (meth)acrylic monomer as a monomer, and light-diffusing fine particles having a lower refractive index than the pressure-sensitive adhesive. However, the adhesive described in Patent Document 2 has a problem in that it has low adhesive strength over a small area and is not suitable for bonding optical films that require fixing over a very small area.
Furthermore, Patent Document 3 describes an adhesive made of a siloxane polymer, but because the resin is flexible, there is a problem in that the resin deforms during adhesion, adversely affecting the optical characteristics.

JP 2014-132092 A JP 2014-224964 A JP 2009-507959 A

The present invention aims to provide an adhesive that can exhibit surface tackiness to improve temporary adhesion, and furthermore, can exhibit excellent adhesive strength by enhancing adhesion even after temporary adhesion, has excellent transparency, and can suppress brightness degradation, particularly when used to bond optical films.

The present invention is an adhesive comprising a thermoplastic resin, a reactive diluent (A), and a photoreaction initiator, wherein the thermoplastic resin is a polyvinyl acetal resin, the reactive diluent (A) has a 90 degree peel adhesion strength of 5.5 N/25 mm or more when used to bond PET sheets together, as measured in accordance with JIS K 6851-1:1999, and the reactive diluent (A) is an adhesive comprising 5 to 85% by weight of a (meth)acrylic acid ester having a cyclic ether structure and 5 to 30% by weight of an epoxy compound.
The present invention will be described in detail below.

The inventors have discovered that by combining a thermoplastic resin, a reactive diluent (A) that satisfies the specified physical properties, and a photoreaction initiator, it is possible to obtain an adhesive that exhibits excellent surface tackiness during one-stage curing and has excellent temporary adhesion. Furthermore, they have discovered that such an adhesive exhibits enhanced adhesion and excellent adhesive strength during two-stage curing, which has led to the completion of the present invention.

The adhesive of the present invention contains a thermoplastic resin.
By including a thermoplastic resin, temporary adhesion to an adherend can be sufficiently improved.

The above thermoplastic resins include polyethylene, polypropylene, ethylene-α-olefin copolymers such as ethylene-propylene copolymers, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol resins, polyvinyl acetal resins, etc. Also included are fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymers, etc. Further included are acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene-ether copolymers (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, etc. Also included are polymethacrylic acid, polymethacrylic acid esters such as polymethacrylic acid methyl ester, polyacrylic acids, polycarbonates, polyphenylene sulfides, silicone resins, etc. Of these, polyvinyl acetal resins and polymethacrylic acid esters are preferred, and polyvinyl acetal resins are more preferred.

The polyvinyl acetal resin has an average degree of polymerization of preferably 100 (lower limit) and 5,000 (upper limit).
The mechanical strength of the obtained cured product can be sufficiently improved when the average polymerization degree of the polyvinyl acetal resin is 100 or more. When the average polymerization degree of the polyvinyl acetal resin is 5000 or less, the solution viscosity can be made suitable during acetalization of polyvinyl alcohol.
The average polymerization degree of the polyvinyl acetal resin is more preferably 600 in the lower limit and 4,500 in the upper limit.

The amount of acetal groups in the polyvinyl acetal resin is preferably 50 mol % in lower limit and 85 mol % in upper limit, regardless of whether an aldehyde is used alone or in combination of two or more kinds.
When the amount of acetal groups in the polyvinyl acetal resin is 50 mol% or more, the coating property of the adhesive can be improved. Also, the compatibility with the reactive diluent can be improved. When the amount of acetal groups in the polyvinyl acetal resin is 85 mol% or less, the mechanical strength of the obtained cured product can be sufficiently improved.
With respect to the amount of acetal groups in the polyvinyl acetal resin, the lower limit is more preferably 54 mol%, even more preferably 58 mol%, and particularly preferably 60 mol%, and the upper limit is more preferably 82 mol%, even more preferably 79 mol%, and particularly preferably 77 mol%.
Regarding the method for calculating the amount of acetal groups, since the acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, the method of counting the two acetalized hydroxyl groups is adopted.
In this specification, when the acetal group is an acetoacetal group, it is also referred to as the amount of acetoacetal groups, and when the acetal group is a butyral group, it is also referred to as the amount of butyral groups.

As a method for adjusting the amount of acetal groups in the polyvinyl acetal, for example, a method for adjusting the amount of the aldehyde added can be mentioned. By decreasing the amount of the aldehyde added, the amount of acetal groups in the polyvinyl acetal decreases, and by increasing the amount of the aldehyde added, the amount of acetal groups in the polyvinyl acetal increases.

The preferred lower limit of the hydroxyl group content of the polyvinyl acetal resin is 16 mol %, and the preferred upper limit is 45 mol %.
When the amount of hydroxyl groups is 16 mol% or more, the mechanical strength of the obtained cured product can be sufficiently improved. In addition, the adhesive strength can be further improved. When the amount of hydroxyl groups is 45 mol% or less, the moisture resistance and weather resistance can be improved. In addition, the temporary adhesion during the first curing step can be improved, and further, the adhesiveness during the second curing step can be improved.
With respect to the amount of hydroxyl groups in the polyvinyl acetal resin, the lower limit is more preferably 20 mol%, more preferably 22 mol%, more preferably 40 mol%, even more preferably 38 mol%, still more preferably 36 mol%, and particularly preferably 35 mol%.

The preferred lower limit of the amount of acetyl groups in the polyvinyl acetal resin is 0.1 mol %, and the preferred upper limit is 30 mol %.
When the amount of acetyl groups is 0.1 mol% or more, the mechanical strength of the obtained cured product can be sufficiently improved. In addition, the compatibility with the reactive diluent can be increased. When the amount of acetyl groups is 30 mol% or less, the temporary adhesion during one-stage curing can be improved, and further, the adhesion during two-stage curing can be improved. In addition, the moisture resistance can be sufficiently improved.
The lower limit of the acetyl group amount is more preferably 0.2 mol %, still more preferably 0.3 mol %, and the upper limit is more preferably 24 mol %, still more preferably 20 mol %, still more preferably 19.5 mol %, and particularly preferably 15 mol %.

An example of a method for adjusting the amount of acetyl groups in the polyvinyl acetal to fall within the above range is to adjust the degree of saponification of the polyvinyl alcohol. That is, the amount of acetyl groups in the polyvinyl acetal depends on the degree of saponification of the polyvinyl alcohol, and if a polyvinyl alcohol with a low degree of saponification is used, the amount of acetyl groups in the polyvinyl acetal becomes large, whereas if a polyvinyl alcohol with a high degree of saponification is used, the amount of acetyl groups in the polyvinyl acetal becomes small.

The polyvinyl acetal resin is preferably a polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol having a saponification degree of 80 mol % or more. By using such a polyvinyl acetal resin, the stability of the adhesive can be improved and excellent mechanical strength can be exhibited for a long period of time.
If the degree of saponification of polyvinyl alcohol is less than 80 mol%, the solubility of polyvinyl alcohol in water decreases, which may make acetalization difficult, and the amount of hydroxyl groups in polyvinyl alcohol is small, which may make the acetalization reaction difficult to proceed.
A more preferred lower limit of the saponification degree of the polyvinyl alcohol is 85 mol %.

The method for the acetalization is not particularly limited, and any conventionally known method can be used. For example, there can be mentioned a method in which an aldehyde is added to an aqueous solution of polyvinyl alcohol in the presence of an acid catalyst such as hydrochloric acid.
The aldehyde is not particularly limited, and examples thereof include formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butylaldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, etc. In addition, examples thereof include furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde, etc.

As the above-mentioned polyvinyl acetal resin, polyvinyl butyral resin in which the acetal group is a butyral group, and polyvinyl acetoacetal resin in which the acetal group is an acetoacetal group are preferred, with polyvinyl acetoacetal resin being more preferred since it can suppress brightness deterioration, particularly when the adhesive is used to bond a prism sheet.

In the adhesive of the present invention, the content of the thermoplastic resin is preferably 5% by weight in the lower limit and 40% by weight in the upper limit.
When the content of the thermoplastic resin is 5% by weight or more, the temporary adhesion during the first curing step can be improved, and when the content of the thermoplastic resin is 40% by weight or less, the cohesive force during the second curing step can be improved to improve the adhesiveness.
The content of the thermoplastic resin is more preferably 10% by weight in the lower limit and 20% by weight in the upper limit.

The adhesive of the present invention contains a reactive diluent (A).
The reactive diluent (A) has a 90 degree peel adhesion strength of 5.5 N/25 mm or more when used to bond PET sheets together, as measured in accordance with JIS K 6851-1:1999.
By including the reactive diluent (A), the temporary adhesion during the first curing step can be improved.
In this specification, the reactive diluent means a diluent that is compatible with the thermoplastic resin and can liquefy the adhesive, and that can react with other reactive diluents to crosslink and harden them by irradiating them with active energy rays.

The reactive diluent (A) may include (meth)acrylic acid esters having a cyclic ether structure, (meth)acrylic acid esters having two or more ester bonds, and (meth)acrylic acid esters having a urethane bond. In addition, epoxy compounds having an alkylene oxide structure, polyfunctional alicyclic epoxy compounds, polyfunctional aliphatic epoxy compounds, aromatic epoxy compounds, etc. may be used alone or in combination. Among them, it is preferable that the reactive diluent (A) contains (meth)acrylic acid esters such as (meth)acrylic acid esters having a cyclic ether structure and (meth)acrylic acid esters having two or more ester bonds, since the temporary adhesion during the first-stage curing can be further improved. In addition to the above (meth)acrylic acid esters, it is more preferable to further contain epoxy compounds such as epoxy compounds having an alkylene oxide structure, polyfunctional alicyclic epoxy compounds, and polyfunctional aliphatic epoxy compounds.

As the (meth)acrylic acid ester having a cyclic ether structure, it is preferable to use a (meth)acrylic acid ester having a cyclic ether structure ranging from a three-membered ring to a six-membered ring.
These may be monomeric esters or polymeric esters, and may be used alone or in combination of two or more kinds.

Examples of the (meth)acrylic acid ester having a three-membered cyclic ether structure include glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate glycidyl ether, 3-hydroxypropyl (meth)acrylate glycidyl ether, etc. Other examples include 4-hydroxybutyl acrylate glycidyl ether, 5-hydroxypentyl (meth)acrylate glycidyl ether, 6-hydroxyhexyl (meth)acrylate glycidyl ether, etc.

Examples of the (meth)acrylic acid ester having a four-membered ring cyclic ether structure include (3-methyloxetan-3-yl)methyl (meth)acrylate, (3-propyloxetan-3-yl)methyl (meth)acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, etc. Other examples include (3-butyloxetan-3-yl)methyl (meth)acrylate, (3-ethyloxetan-3-yl)ethyl (meth)acrylate, (3-ethyloxetan-3-yl)propyl (meth)acrylate, (3-ethyloxetan-3-yl)butyl (meth)acrylate, etc. Further examples include (3-ethyloxetan-3-yl)pentyl (meth)acrylate, (3-ethyloxetan-3-yl)hexyl (meth)acrylate, etc.

Examples of the (meth)acrylic acid ester having a five-membered ring cyclic ether structure include tetrahydrofurfuryl (meth)acrylate, γ-butyrolactone (meth)acrylate, (2,2-dimethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, etc. Other examples include (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (2-methyl-2-isobutyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (2-cyclohexyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, etc. Furthermore, tetrahydrofurfuryl alcohol acrylic acid polymer ester can also be used.

Examples of the (meth)acrylic acid ester having a six-membered cyclic ether structure include tetrahydro-2H-pyran-2-yl-(meth)acrylate, 2-{1-[(tetrahydro-2H-pyran-2-yl)oxy]-2-methylpropyl}(meth)acrylate, etc. Other examples include cyclic trimethylolpropane formal acrylate, (meth)acryloylmorpholine, etc.

As the (meth)acrylic acid ester having the above-mentioned cyclic ether structure, those having a five-membered ring or more are preferably used, since adhesion is further improved by dissolving the polycarbonate surface, particularly when a polycarbonate substrate is used as the plastic substrate. Among them, tetrahydrofurfuryl (meth)acrylate, tetrahydrofurfuryl alcohol acrylic acid polymer ester, and (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate are more preferred, since they have excellent solubility and can further improve adhesion to the polycarbonate substrate.

Examples of (meth)acrylic acid esters having two or more ester bonds include polyfunctional (meth)acrylic acid esters having two or more ester bonds derived from (meth)acrylic acid, and (meth)acrylic acid esters having ester bonds other than ester bonds derived from (meth)acrylic acid. Specific examples include lactone-modified (meth)acrylate compounds obtained by reacting a (meth)acrylic acid ester with a lactone compound, and polyester (meth)acrylate compounds obtained by reacting a polyester polyol with (meth)acrylic acid.

In the lactone-modified (meth)acrylate compound obtained by reacting the (meth)acrylic acid ester with a lactone compound, examples of the (meth)acrylic acid ester include an aliphatic (meth)acrylate compound and an aromatic (meth)acrylate compound.
Examples of the aliphatic (meth)acrylate compound include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, glycerin diacrylate, trimethylolpropane diacrylate, pentaerythritol triacrylate, and dipentaerythritol pentaacrylate.
Examples of the aromatic (meth)acrylate compound include 4-hydroxyphenyl acrylate, β-hydroxyphenethyl acrylate, 4-hydroxyphenethyl acrylate, 1-phenyl-2-hydroxyethyl acrylate, 3-hydroxy-4-acetylphenyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, etc. Examples of the lactone compound include ε-caprolactone, γ-butyrolactone, etc.

In the polyester (meth)acrylate compound obtained by reacting the above polyester polyol with (meth)acrylic acid, the above polyester polyol is composed of a polybasic acid and a polyhydric alcohol.

Examples of the polybasic acid include aliphatic dibasic acids, alicyclic dibasic acids, aromatic dibasic acids, aliphatic tribasic acids, aromatic tribasic acids, and anhydrides thereof.
Examples of the aliphatic dibasic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, and icosane diacid. Examples of the alicyclic dibasic acids include hexahydrophthalic acid and 1,4-cyclohexanedicarboxylic acid. Examples of the aromatic dibasic acids include phthalic acid, terephthalic acid, isophthalic acid, and orthophthalic acid. Examples of the aliphatic tribasic acids include 1,2,5-hexanetricarboxylic acid and 1,2,4-cyclohexanetricarboxylic acid. Examples of the aromatic tribasic acid include trimellitic acid, trimellitic anhydride, 1,2,5-benzenetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid.

Examples of the polyhydric alcohol include dihydric alcohols and trihydric or higher polyhydric alcohols.
Examples of the dihydric polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2,2-trimethyl-1,3-propanediol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, and 3-methyl-1,3-butanediol. Examples of the trihydric or higher polyhydric alcohol include trimethylolethane, trimethylolpropane, glycerin, hexanetriol, and pentaerythritol. Examples of the polyhydric alcohol include modified polyether polyols obtained by ring-opening polymerization of the dihydric polyhydric alcohol or the trihydric or higher polyhydric alcohol and a cyclic ether bond-containing compound. Examples of the cyclic ether bond-containing compound include ethylene oxide, propylene oxide, tetrahydrofuran, ethyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, etc. Furthermore, lactone-modified polyester polyols obtained by polycondensation reaction of the dihydric polyalcohols or trihydric or higher polyalcohols with the lactone compounds may be used.

By using the (meth)acrylic acid ester having two or more ester bonds, adhesion to plastics can be improved.
The acid value of the (meth)acrylic acid ester having two or more ester bonds has a preferred lower limit of 20 mgKOH/g.
When the acid value is 20 mgKOH/g or more, the adhesion can be further improved.
A more preferable lower limit of the acid value is 100 mgKOH/g.
The upper limit of the acid value is not particularly limited, but a preferred upper limit is 500 mgKOH/g, and a more preferred upper limit is 300 mgKOH/g.

Examples of the (meth)acrylic acid ester having the above-mentioned urethane bond include those obtained by reacting an isocyanate compound with a (meth)acrylic acid derivative having a hydroxyl group.

Examples of isocyanate compounds that are the raw material for the (meth)acrylic acid ester having the above urethane bond include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc. In addition, examples of the isocyanate compounds include diphenylmethane-4,4'-diisocyanate (MDI), hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, norbornane diisocyanate, tolidine diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, lysine diisocyanate, triphenylmethane triisocyanate, etc. In addition, examples of the isocyanate compounds include tris(isocyanatephenyl)thiophosphate, tetramethylxylylene diisocyanate, 1,6,11-undecane triisocyanate, etc.

Furthermore, as the above-mentioned isocyanate compound, for example, a chain-extended isocyanate compound obtained by reacting a polyol such as ethylene glycol, propylene glycol, glycerin, sorbitol, polyether diol, polyester diol, polycaprolactone diol, etc. with an excess of an isocyanate compound can also be used.

Examples of (meth)acrylic acid derivatives having a hydroxyl group that serve as raw materials for the (meth)acrylic acid esters having urethane bonds include mono(meth)acrylates of dihydric alcohols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and polyethylene glycol. Other examples include mono(meth)acrylates or di(meth)acrylates of trihydric alcohols such as trimethylolethane, trimethylolpropane, and glycerin, and epoxy(meth)acrylates such as bisphenol A-type epoxy(meth)acrylate.

Examples of the alkylene oxide group contained in the epoxy compound having an alkylene oxide structure include an oxymethylene group, an oxyethylene group, an oxypropylene group, and an oxybutylene group.
The number of moles of the alkylene oxide structure added is preferably 1 to 10.
Examples of the epoxy compound having an alkylene oxide structure include alkylene oxide adducts of bisphenol F type epoxy resins, alkylene oxide adducts of bisphenol A type epoxy resins, glycidyl ether adducts of polyethylene glycol, and glycidyl ether adducts of polypropylene glycol.

Examples of the above-mentioned polyfunctional alicyclic epoxy compounds include cyclopentadiene type epoxy compounds, dicyclopentadiene type epoxy compounds such as dicyclopentadiene dimethanol diglycidyl ether, etc.

The above-mentioned polyfunctional aliphatic epoxy compounds include trimethylolpropane diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, propylene glycol diglycidyl ether, etc. Further examples include neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, glycerin triglycidyl ether, polyglycerol triglycidyl ether, diglycerol triglycidyl ether, etc.

As the reactive diluent (A), (meth)acrylic acid esters having two or more ester bonds, (meth)acrylic acid esters having a cyclic ether structure, polyfunctional alicyclic epoxy compounds, and epoxy compounds having an alkylene oxide structure are more preferably used. Among them, lactone-modified (meth)acrylate compounds, (meth)acrylic acid esters having a cyclic ether structure of five or more members, dicyclopentadiene-type epoxy compounds, and alkylene oxide adducts of bisphenol A-type epoxy resins are particularly preferably used.

The content of the (meth)acrylic acid ester having two or more ester bonds in the reactive diluent (A) is preferably 30% by weight, more preferably 50% by weight, more preferably 85% by weight, and more preferably 70% by weight.

The content of the (meth)acrylic acid ester having the above-mentioned cyclic ether structure in the above-mentioned reactive diluent (A) is preferably at least 5% by weight, more preferably at least 15% by weight, more preferably at least 85% by weight, and more preferably at least 50% by weight.

The content of the epoxy compound in the reactive diluent (A) is preferably 5% by weight at the lower limit, more preferably 10% by weight at the lower limit, preferably 30% by weight at the upper limit, and more preferably 25% by weight at the upper limit.

In the adhesive of the present invention, the content of the reactive diluent (A) is preferably 30% by weight in the lower limit and 85% by weight in the upper limit.
When the content of the reactive diluent (A) is 30% by weight or more, the temporary adhesion during the first curing step can be improved, and when the content of the reactive diluent (A) is 85% by weight or less, the adhesion during the second curing step can be improved.
The content of the reactive diluent (A) is more preferably 50% by weight in the lower limit and 70% by weight in the upper limit.

In the adhesive of the present invention, the content of the (meth)acrylic acid ester having two or more of the above-mentioned ester bonds has a preferred lower limit of 0 weight%, a more preferred lower limit of 10 weight%, an even more preferred lower limit of 30 weight%, a preferred upper limit of 85 weight%, a more preferred upper limit of 75 weight%, and an even more preferred upper limit of 65 weight%.

In the adhesive of the present invention, the content of the (meth)acrylic acid ester having the above-mentioned cyclic ether structure has a preferred lower limit of 0 weight%, a more preferred lower limit of 5 weight%, an even more preferred lower limit of 15 weight%, a preferred upper limit of 85 weight%, a more preferred upper limit of 65 weight%, and an even more preferred upper limit of 50 weight%.

In the adhesive of the present invention, the content of the above epoxy compound has a preferred lower limit of 0 weight%, a more preferred lower limit of 5 weight%, an even more preferred lower limit of 10 weight%, a preferred upper limit of 35 weight%, a more preferred upper limit of 30 weight%, and an even more preferred upper limit of 25 weight%.

In the adhesive of the present invention, the ratio of the content (mol) of the thermoplastic resin to the content (mol) of the diluent (A) (content of thermoplastic resin/content of diluent (A)) has a preferred lower limit of 0.0003, a more preferred lower limit of 0.0009, a preferred upper limit of 0.004, and a more preferred upper limit of 0.002.
The contents (moles) of the thermoplastic resin and diluent (A) can be calculated based on the molecular weights and the amounts of the thermoplastic resin and diluent (A) added. When the thermoplastic resin is a polyvinyl acetal resin, the molecular weight of the polyvinyl acetal resin can be calculated based on the average degree of polymerization, the amount of acetal groups, the amount of hydroxyl groups, the amount of acetyl groups, and the molecular weight of each constituent unit.

In the adhesive of the present invention, the ratio of the total number of acetal groups to the total number of functional groups ((meth)acrylic groups or epoxy groups) of the diluent (A) (number of acetal groups/number of functional groups of diluent (A)) is preferably 0.13 in its lower limit, more preferably 0.18 in its upper limit, and more preferably 0.70 in its upper limit, both of which are 0.40.
The total number of acetal groups can be calculated based on the molecular weight, average degree of polymerization, and amount of acetal groups of the polyvinyl acetal resin, and the amount of polyvinyl acetal resin added in the adhesive of the present invention.
The total number of functional groups in the diluent (A) can be calculated based on the molecular weight of the diluent (A), the number of functional groups in one molecule of the diluent (A), and the amount of diluent (A) added in the adhesive of the present invention.

In the adhesive of the present invention, the ratio of the molecular weight of the thermoplastic resin to the functional group equivalent of the diluent (A) (molecular weight per (meth)acrylic group or epoxy group) (molecular weight of thermoplastic resin/functional group equivalent of diluent (A)) is preferably 80 in the lower limit, more preferably 180 in the lower limit, and preferably 300 in the upper limit, more preferably 250 in the upper limit.
The functional group equivalent of the diluent (A) can be calculated based on the molecular weight of the diluent (A) and the number of functional groups in one molecule of the diluent (A).
Furthermore, when the diluent (A) contains a plurality of diluents, the functional group equivalent of the diluent (A) can be calculated based on the amount of the diluent (A) added in the adhesive of the present invention and the total number of functional groups of the diluent (A).

The adhesive of the present invention preferably contains, in addition to the reactive diluent (A), a reactive diluent (B) other than the reactive diluent (A).
That is, the reactive diluent (B) has a 90 degree peel adhesion strength of less than 5.5 N/25 mm when used to bond PET sheets together, as measured in accordance with JIS K 6851-1:1999.
By including the reactive diluent (B), the adhesiveness during the two-stage curing can be further improved.

The reactive diluent (B) may be a (meth)acrylic acid ester other than the reactive diluent (A), an epoxy compound, etc. Examples of the reactive diluent (B) include a (meth)acrylic acid ester having an alkylene oxide structure having 1 to 3 carbon atoms, an (meth)acrylic acid alkyl ester, a (meth)acrylic acid ester having a polar group, an acryloyl group-containing polyvalent carboxylic acid ester, an aromatic epoxy compound, etc.

Examples of the alkylene oxide group contained in the (meth)acrylic acid ester having an alkylene oxide structure having 1 to 3 carbon atoms include an oxymethylene group and an oxyethylene group.
The number of moles of the alkylene oxide structure added is preferably 1 to 10.
Examples of the (meth)acrylic acid ester having an alkylene oxide structure include methoxypolyethylene glycol (meth)acrylate and ethoxypolyethylene glycol (meth)acrylate.

The above-mentioned (meth)acrylic acid alkyl esters include, for example, (meth)acrylic acid esters having an alkyl group having 1 to 20 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, etc. Further examples include n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, etc.

Examples of the (meth)acrylic acid ester having a polar group include (meth)acrylic acid esters having a hydroxyl group, an amide group, an amino group, an isocyanate group, or the like as the polar group.
Examples of the (meth)acrylic acid ester having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (meth)acrylic acid esters of polyethylene glycol, and glycerol (meth)acrylate.
Examples of the (meth)acrylic acid ester having an amide group include N,N-dimethylaminopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acryloylmorpholine, N-isopropyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide.
Examples of (meth)acrylic acid esters having an amino group include N-dialkylaminoalkyl(meth)acrylamide, N,N-dialkylaminoalkyl(meth)acrylamide, etc. Specific examples include N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-di-t-butylaminoethyl(meth)acrylate, N,N-dimethylaminobutyl(meth)acrylate, etc. Further examples include N,N-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, etc.
An example of the (meth)acrylic acid ester having an isocyanate group is 2-isocyanatoethyl (meth)acrylate.
Examples of the acryloyl group-containing polyvalent carboxylic acid ester include 2-acryloyloxyethyl succinate.

Examples of the aromatic epoxy compounds include bisphenol A type glycidyl ether epoxy resins, bisphenol F type glycidyl ether epoxy resins, phenol novolac type glycidyl ether epoxy resins, etc.

As the reactive diluent (B), methoxypolyethylene glycol (meth)acrylate, (meth)acrylic acid ester having an amide group, acryloyl group-containing polycarboxylic acid ester, and aromatic epoxy compound are preferably used. It is also preferable to use a combination of (meth)acrylic acid ester having an alkylene oxide structure with 1 to 3 carbon atoms, (meth)acrylic acid alkyl ester, and (meth)acrylic acid ester having a polar group.

In the adhesive of the present invention, the content of the reactive diluent (B) is preferably at a lower limit of 10% by weight, more preferably at a lower limit of 20% by weight, preferably at an upper limit of 40% by weight, and more preferably at an upper limit of 30% by weight.

In the adhesive of the present invention, the content of the (meth)acrylic acid ester having the alkylene oxide structure having 1 to 3 carbon atoms has a preferred lower limit of 5 weight%, a more preferred lower limit of 10 weight%, a preferred upper limit of 25 weight%, and a more preferred upper limit of 20 weight%.

In the adhesive of the present invention, the content of the above-mentioned (meth)acrylic acid alkyl ester has a preferred lower limit of 5 weight percent, a more preferred lower limit of 10 weight percent, a preferred upper limit of 20 weight percent, and a more preferred upper limit of 15 weight percent.

In the adhesive of the present invention, the content of the (meth)acrylic acid ester having the above-mentioned polar group has a preferred lower limit of 2 weight%, a more preferred lower limit of 4 weight%, a preferred upper limit of 10 weight%, and a more preferred upper limit of 7 weight%.

In the adhesive of the present invention, the content of the reactive diluent (B) relative to 100 parts by weight of the reactive diluent (A) has a preferred lower limit of 0 parts by weight, a more preferred lower limit of 10 parts by weight, a preferred upper limit of 50 parts by weight, and a more preferred upper limit of 30 parts by weight.

In the adhesive of the present invention, the ratio of the content (mol) of the thermoplastic resin to the total content (mol) of the diluents (A) and (B) (content of thermoplastic resin/total content of diluents (A) and (B)) has a preferred lower limit of 0.0002, a more preferred lower limit of 0.00075, a preferred upper limit of 0.3, and a more preferred upper limit of 0.0015.

In the adhesive of the present invention, the ratio of the total number of acetal groups to the total number of functional groups ((meth)acrylic groups or epoxy groups) of diluents (A) and (B) (number of acetal groups/number of functional groups of diluents (A) and (B)) has a preferred lower limit of 0.05, a more preferred lower limit of 0.13, a preferred upper limit of 0.6, and a more preferred upper limit of 0.2.

The ratio of the total number of epoxy groups to the total number of (meth)acrylic groups in the adhesive of the present invention (number of epoxy groups/number of (meth)acrylic groups) has a preferred lower limit of 0.05, a more preferred lower limit of 0.2, a preferred upper limit of 0.5, and a more preferred upper limit of 0.3.

In the adhesive of the present invention, the ratio of the molecular weight of the thermoplastic resin to the functional group equivalent of the diluents (A) and (B) (molecular weight of thermoplastic resin/functional group equivalent of diluents (A) and (B)) is preferably 110 in the lower limit, more preferably 140 in the lower limit, and more preferably 300 in the upper limit, and more preferably 190 in the upper limit.
The functional group equivalents of the diluents (A) and (B) can be calculated based on the amounts of the diluents (A) and (B) added in the adhesive of the present invention and the total number of functional groups in the diluents (A) and (B).

The adhesive of the present invention contains a photoinitiator.
Specific examples of the photoreaction initiator include acylphosphine oxide-based photoreaction initiators, titanocene-based photoreaction initiators, acetophenone-based photoreaction initiators, benzoin-based photoreaction initiators, benzophenone-based photoreaction initiators, thioxanthone-based photoreaction initiators, and sulfonium salt-based photoreaction initiators.
Examples of the acylphosphine oxide photoinitiator include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.
Examples of the titanocene-based photoreaction initiator include bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium.
Examples of the acetophenone-based photoreaction initiator include 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 1,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, and 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomer.
Examples of the benzoin-based photoreaction initiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether.
Examples of the benzophenone-based photoinitiator include benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, 2,4,6-trimethylbenzophenone, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy)ethyl]benzenemethanaminium bromide, and (4-benzoylbenzyl)trimethylammonium chloride.
Examples of the thioxanthone-based photoinitiator include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-(3-dimethylamino-2-hydroxy)-3,4-dimethyl-9H-thioxanthone-9-one mesochloride, and the like.
The sulfonium salt photoinitiator may, for example, be tris(4-(4-acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate.
These photoreaction initiators may be used alone or in combination of two or more kinds.

These auxiliary agents include triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, and ethyl 4-dimethylaminobenzoate. It is also possible to use in combination with 4-dimethylaminobenzoate (n-butoxy)ethyl, 4-dimethylaminobenzoate isoamyl, 4-dimethylaminobenzoate 2-ethylhexyl, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, and the like.

Among these, it is preferable to use 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, benzoyl isopropyl ether, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and tris(4-(4-acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate.

In the adhesive of the present invention, the content of the photoreaction initiator has a preferred lower limit of 0.01% by weight and a preferred upper limit of 10% by weight. When the content of the photoreaction initiator is within this range, the resulting adhesive has better photocurability and storage stability. A more preferred lower limit of the content of the photoreaction initiator is 0.1% by weight and a more preferred upper limit is 5% by weight.

Additionally, the adhesive of the present invention may further contain a non-reactive component.
In this specification, the term "non-reactive component" refers to a compound that is compatible with the above-mentioned thermoplastic resin and does not contain a reactive double bond, or a compound that has a reactive double bond but does not substantially exhibit polymerization reactivity.
Specific examples of the non-reactive component include plasticizers such as organic acid esters, organic phosphates, and organic phosphites, tackifiers such as rosin resins and terpene resins, and solventless acrylic polymers. Examples of the plasticizer include organic acid ester plasticizers such as monobasic organic acid esters and polybasic organic acid esters, and phosphoric acid plasticizers such as organic phosphoric acid plasticizers and organic phosphites. Among these, organic acid ester plasticizers are preferred. These plasticizers may be used alone or in combination of two or more. The plasticizer is preferably a liquid plasticizer.

Examples of the organic acid ester include monobasic organic acid esters and polybasic organic acid esters.
The monobasic organic acid ester is not particularly limited, and examples thereof include glycol esters obtained by reacting a monobasic organic acid such as butyric acid, isobutyric acid, caproic acid, 2-ethylbutyric acid, heptyl acid, n-octylic acid, 2-ethylhexyl acid, pelargonic acid (n-nonylic acid), or decylic acid with a glycol such as triethylene glycol, tetraethylene glycol, or tripropylene glycol.
The polybasic organic acid ester is not particularly limited, and examples thereof include ester compounds obtained by reacting a polybasic organic acid such as adipic acid, sebacic acid, or azelaic acid with an alcohol having a linear or branched structure having 4 to 8 carbon atoms.

Specific examples of the organic acid esters include triethylene glycol di-2-ethylbutyrate (3GH), triethylene glycol di-2-ethylhexanoate (3GO), triethylene glycol dicaprylate, triethylene glycol di-n-octanoate, and triethylene glycol di-n-heptanoate (3G7). In addition, tetraethylene glycol di-n-heptanoate (4G7), tetraethylene glycol di-2-ethylhexanoate, dibutyl sebacate, dioctyl azelate, dibutyl carbitol adipate, ethylene glycol di-2-ethylbutyrate, and 1,3-propylene glycol di-2-ethylbutyrate. In addition, 1,4-butylene glycol di-2-ethylbutyrate, diethylene glycol di-2-ethylbutyrate, diethylene glycol di-2-ethylhexanoate, and dipropylene glycol di-2-ethylbutyrate are also included. Also included are triethylene glycol di-2-ethylpentanoate, tetraethylene glycol di-2-ethylbutyrate (4GH), diethylene glycol dicapryate, dihexyl adipate (DHA), dioctyl adipate, hexylcyclohexyl adipate, diisononyl adipate, heptylnonyl adipate, etc. Other examples include oil-modified sebacic acid alkyd, a mixture of a phosphate ester and an adipate ester, and a mixed adipate ester made from an alkyl alcohol having 4 to 9 carbon atoms and a cyclic alcohol having 4 to 9 carbon atoms. Among these, DHA, 3GO, 4GO, 3GH, 4GH, and 3G7 are preferred. Also, 3GH, 3G7, and 3GO are more preferred, and 3GO is even more preferred.

The organic phosphate ester or organic phosphite ester may be a compound obtained by a condensation reaction between phosphoric acid or phosphorous acid and an alcohol. Among them, a compound obtained by a condensation reaction between an alcohol having 1 to 12 carbon atoms and phosphoric acid or phosphorous acid is preferred. Examples of the alcohol having 1 to 12 carbon atoms include methanol, ethanol, butanol, hexanol, 2-ethylbutanol, heptanol, octanol, 2-ethylhexanol, decanol, dodecanol, butoxyethanol, butoxyethoxyethanol, and benzyl alcohol.
Examples of the organic phosphate ester or organic phosphite ester include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(2-ethylhexyl) phosphate, tri(butoxyethyl) phosphate, tri(2-ethylhexyl) phosphite, isodecylphenyl phosphate, and triisopropyl phosphate.

The rosin-based resin includes, for example, rosin diol.
The rosin diol is not particularly limited as long as it is a rosin-modified diol having two rosin skeletons and two hydroxyl groups in the molecule. Diols having a rosin component in the molecule are called rosin polyols, and these include polyether types such as polypropylene glycol (PPG) in which the skeleton excluding the rosin component is polyether, and polyester types such as condensation polyester polyols, lactone polyester polyols, and polycarbonate diols.
Examples of the rosin diol include rosin ester obtained by reacting rosin with a polyhydric alcohol, epoxy-modified rosin ester obtained by reacting rosin with an epoxy compound, and modified rosin having a hydroxyl group, such as polyether having a rosin skeleton, etc. These can be produced by conventionally known methods.

Examples of the rosin component include abietic acid and pimaric acid type resin acids such as dehydroabietic acid, dihydroabietic acid, tetrahydroabietic acid, diabietic acid, neoabietic acid, and levopimaric acid, which are derivatives of abietic acid, hydrogenated rosins obtained by hydrogenating these acids, and disproportionated rosins obtained by disproportionating these acids.
Commercially available rosin resins include, for example, Pine Crystal D-6011, KE-615-3, KR-614, KE-100, KE-311, KE-359, KE-604, and D-6250 manufactured by Arakawa Chemical Industries Co., Ltd.

Examples of the terpene resin include terpene phenol resins.
The terpene phenol resin is a copolymer of phenol and a terpene resin, which is an essential oil component obtained from natural products such as rosin and orange peel, and also includes partially hydrogenated terpene phenol resins in which at least a portion of the copolymer is hydrogenated, and fully hydrogenated terpene phenol resins in which the copolymer is completely hydrogenated.
Here, the fully hydrogenated terpene phenolic resin is a terpene resin (tackifier resin) obtained by substantially completely hydrogenating a terpene phenolic resin, and the partially hydrogenated terpene phenolic resin is a terpene resin (tackifier resin) obtained by partially hydrogenating a terpene phenolic resin. The terpene phenolic resin has a double bond derived from a terpene and an aromatic ring double bond derived from a phenol. Therefore, the fully hydrogenated terpene phenolic resin means a tackifier resin in which both the terpene moiety and the phenol moiety are completely or almost hydrogenated, and the partially hydrogenated terpene phenolic resin means a terpene phenolic resin in which the degree of hydrogenation of these moieties is partial, not complete. The hydrogenation method and reaction form are not particularly limited.
An example of a commercially available product of the terpene phenol resin is YS Polystar NH (fully hydrogenated terpene phenol resin) manufactured by Yasuhara Chemical Co., Ltd.

Examples of the solvent-free acrylic polymer include a polymer of at least one monomer selected from (meth)acrylic acid alkyl esters having an alkyl group with 1 to 20 carbon atoms, and a copolymer of the monomer and another copolymerizable monomer.
Commercially available solvent-free acrylic polymers include, for example, ARUFON-UP1000 series, UH2000 series, and UC3000 series manufactured by Toagosei Co., Ltd.

Furthermore, the adhesive of the present invention may contain various additives as other optional components, provided that the additives do not impair the object and effect of the present invention.
Examples of the additives include adhesion regulators, tackifier resins, plasticizers, emulsifiers, softeners, fine particles, fillers, pigments, dyes, silane coupling agents, antioxidants, surfactants, and waxes.

The adhesive of the present invention is preferably irradiated with active energy rays at a dose of 3000 mJ/cm ² and cured, and the cured product has a modulus of elasticity of 1×10 ⁵ Pa or more in dynamic viscoelasticity measurement.
When the elastic modulus of the cured product is 1×10 ⁵ Pa or more, the prisms can be grounded without being buried, and the brightness can be improved.
The elastic modulus is more preferably 5×10 ⁵ Pa at its lower limit, more preferably 5×10 ⁷ Pa at its upper limit, and even more preferably 5×10 ⁶ Pa at its upper limit.
The elastic modulus can be measured, for example, by using a dynamic viscoelasticity measuring device.
The elastic modulus mentioned above means the elastic modulus at 50°C.

The adhesive of the present invention is preferably irradiated with active energy rays at a dose of 3000 mJ/cm ² and cured, and the cured product has a tan δ peak temperature derived from the thermoplastic resin of 50° C. or higher.
When the tan δ peak temperature is 50° C. or higher, the luminance can be maintained even when pressure is applied.
The tan δ peak temperature is more preferably 60°C in lower limit, 80°C in upper limit and more preferably 70°C in upper limit.
The tan δ peak temperature can be measured, for example, by using a dynamic viscoelasticity measuring device.

The adhesive of the present invention can be prepared by mixing a thermoplastic resin, a reactive diluent (A), a photoreaction initiator, and, if necessary, a reactive diluent (B), a stabilizer, etc.

The adhesive of the present invention can be used as an adhesive between the same or different materials, such as fibers, composite materials, ceramics, glass, rubber, concrete, paper, metals, and plastics.
Specifically, it can be used for manufacturing building materials such as wallpaper, laminated plywood, and security glass, manufacturing window glass with UV cut filters for automobiles, etc., adhering labels to bottles, cans, bottles, etc. for beverages, adhering exhibits to show windows, etc., adhering optical disk substrates, adhering non-contact IC cards, adhering IC chips, adhering cover glass for organic EL lighting, etc. It can also be used for adhering display members such as projection televisions and organic EL displays whose sealing structure is a completely solid structure, adhering touch panels to liquid crystal panels, and adhering touch panels to front windows, touch panel interiors, etc. It can also be suitably used for adhering various materials and members such as various optical films used in flat panel displays, and laminates used in electrical circuits, and for manufacturing laminates. Examples of the optical film include brightness enhancement films, prism sheets, light diffusion sheets, Fresnel lenses, lenticular lenses, polarizing films, retardation films, color filters, light guide plates, anti-glare films, anti-reflection films, reflective sheets, near-infrared cut filters, viewing angle control films, and viewing angle compensation films.
The adhesive of the present invention can be preferably used for bonding plastics, and has excellent temporary adhesion when cured in one stage, and further exhibits excellent adhesion due to enhanced adhesion when cured in two stages, making it particularly suitable for bonding optical films such as prism sheets which require bonding over an extremely small area.

The method of bonding adherends using the adhesive of the present invention is not particularly limited. For example, a method including a step of applying the adhesive of the present invention to a first member, a step of bonding the first member and a second member together and pressing them together (bonding step), a step of irradiating active energy rays to bond them temporarily after the bonding step (one-stage curing step), and a step of further irradiating active energy rays to bond them after the one-stage curing step (two-stage curing step) is preferred.

When applying the above adhesive to the substrate, for example, a reverse coater, gravure coater (direct, reverse or offset), bar reverse coater, roll coater, die coater, bar coater, rod coater, etc. can be used, or application can be performed by dipping.

For the lamination and pressure bonding, for example, a roll laminator or the like can be used, and the pressure is selected from the range of 0.1 to 10 MPa.
For the above-mentioned active energy ray irradiation, light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and γ-rays, as well as electron beams, proton beams, neutron beams, etc. can be used. However, curing by ultraviolet irradiation is advantageous in terms of curing speed, ease of availability of irradiation equipment, cost, etc.

As a light source for the above-mentioned ultraviolet irradiation, a high pressure mercury lamp, an electrodeless lamp, an extra-high pressure mercury lamp, a carbon arc lamp, a xenon lamp, a metal halide lamp, a chemical lamp, a black light, an LED, or the like can be used.
The integrated exposure amount during ultraviolet irradiation is preferably 2 to 3000 mJ/cm ² , and more preferably 10 to 2000 mJ/cm ² .

In particular, in the case of the high pressure mercury lamp, the irradiation is preferably performed under conditions of 5 to 3000 mJ/cm ² , more preferably 50 to 2000 mJ/cm ² .
In the case of the electrodeless lamp, the irradiation is preferably performed under conditions of 2 to 2000 mJ/cm ² , more preferably 10 to 1000 mJ/cm ² .

The irradiation time varies depending on the type of light source, the distance between the light source and the coating surface, the coating thickness, and other conditions, but is usually several seconds to several tens of seconds, and in some cases may be a fraction of a second. On the other hand, in the case of the above-mentioned electron beam irradiation, it is preferable to use an electron beam having an energy in the range of 50 to 1000 keV, for example, and to set the irradiation dose at 2 to 50 Mrad.

According to the present invention, it is possible to provide an adhesive that exhibits surface tackiness to improve temporary adhesion, and furthermore, that is capable of exhibiting excellent adhesive strength even after temporary adhesion due to enhanced adhesion, has excellent transparency, and is capable of suppressing brightness degradation, particularly when used to bond optical films.

The present invention will be described in more detail below with reference to the following examples, but the present invention is not limited to these examples.

( Reference Examples 1 to 4, 6 to 7, Examples 8 to 9, 12 and 13)
240 g of polyvinyl alcohol (degree of polymerization: 650, degree of saponification: 99 mol%) was added to 1800 g of pure water and dissolved by stirring for 2 hours at 90° C. This solution was cooled to 40° C., and 170 g of hydrochloric acid having a concentration of 35% by weight and 275 g of n-butylaldehyde were added. The liquid temperature was maintained at 40° C. to carry out an acetalization reaction, and the reaction product was precipitated.
Thereafter, the liquid temperature was maintained at 40° C. for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried in a conventional manner to obtain a polyvinyl butyral resin powder.
The resulting polyvinyl butyral resin was dissolved in DMSO-D ₆ (dimethyl sulfoxide) and measured by ¹³ C-NMR (nuclear magnetic resonance spectroscopy), which revealed that it had a hydroxyl group content of 34 mol %, a butyral group content of 65 mol %, and an acetyl group content of 1 mol %.

The obtained polyvinyl butyral resin was used as the thermoplastic resin, and an adhesive was prepared by adding the thermoplastic resin, reactive diluent (A), reactive diluent (B) and photoreaction initiator as shown in Table 1.

The reactive diluent (A), reactive diluent (B) and photoreaction initiator used were as follows: For reactive diluent (A) and reactive diluent (B), the peel adhesive strength was measured in accordance with JIS K 6854-1:1999 under the conditions of a peel angle of 90 degrees and a peel speed of 300 mm/min when PET films were bonded together.
<Reactive Diluent (A)>
[(Meth)acrylate]
M-5300: ω-carboxy-polycaprolactone (n≒2) monoacrylate, manufactured by Toagosei Co., Ltd., molecular weight 300.3, 90 degree peel adhesive strength 6.2 N/25 mm, acid value 230 mg KOH/g
Viscoat #150D: Tetrahydrofurfuryl alcohol acrylic acid polymer ester, manufactured by Osaka Organic Chemical Industry Co., Ltd., molecular weight 156.2, 90 degree peel adhesion strength 8.5 N/25 mm
MEDOL-10: (2-methyl-2-ethyl-1,3-dioxolan-4-yl) methyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd., molecular weight 208.3, 90 degree peel adhesion strength 10.5 N/25 mm
[Epoxy compound]
EP-4088: dicyclopentadiene dimethanol diglycidyl ether, manufactured by ADEKA Corporation, molecular weight 340, 90 degree peel adhesion strength 6.4 N/25 mm
EP-4003S: Propylene oxide adduct of bisphenol A type epoxy resin, manufactured by ADEKA Corporation, molecular weight 940, 90 degree peel strength 7.3 N/25 mm
<Reactive Diluent (B)>
[(Meth)acrylate]
M-90G: Methoxypolyethylene glycol #400 methacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 468, 90 degree peel adhesive strength 2.5 N/25 mm
DMAA: N,N-dimethylacrylamide, manufactured by KJ Chemicals, molecular weight 99.1, 90 degree peel adhesive strength 0.17 N/25 mm
A-SA: 2-acryloyloxyethyl succinate, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 216, 90 degree peel adhesive strength 1.3 N/25 mm
EHA: 2-ethylhexyl acrylate, manufactured by Nippon Shokubai Co., Ltd., molecular weight 184.3, 90 degree peel adhesion strength 4.5 N/25 mm
[Epoxy compound]
EXA-830CRP: Bisphenol F type epoxy resin, manufactured by DIC Corporation, molecular weight 316, 90°C peel strength 1.1 N/25 mm
<Photoinitiator>
Irgacure 184: 1-hydroxycyclohexyl phenyl ketone, manufactured by BASF Irgacure 290: tris(4-(4-acetylphenyl)thiophenyl)sulfonium tetrakis(pentafluorophenyl)borate, manufactured by BASF

( Reference Example 5)
As the polymerizable monomer, 75 parts by weight of methyl methacrylate and 25 parts by weight of methyl acrylate were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a cooling tube, and further, 300 parts by weight of ethyl acetate was added as a polymerization solvent. Next, nitrogen gas was blown in for 30 minutes while stirring to replace the inside of the reaction vessel with nitrogen, and then the reaction vessel was heated to 80°C while stirring. The mixture was left at 80°C for 30 minutes, and further, 0.5 parts by weight of t-butylperoxy-2-ethylhexanoate (1-hour half-life temperature: 92.1°C, 10-hour half-life temperature: 72.1°C) was diluted with 5 parts by weight of ethyl acetate as a polymerization initiator, and the obtained polymerization initiator solution was added dropwise to the reaction vessel over 6 hours to react. The reaction liquid was further cooled to obtain an MMA/MA copolymer having an average molecular weight of 50,000.
The obtained copolymer was used as a thermoplastic resin, and an adhesive was prepared by adding a thermoplastic resin, a reactive diluent (A), a reactive diluent (B), and a photoreaction initiator as shown in Table 1.

( Reference Example 10 and Example 11)
200 g of polyvinyl alcohol with a degree of polymerization of 560 and a degree of saponification of 99 mol% was added to 1800 g of pure water and dissolved by stirring for about 2 hours at a temperature of 90° C. This solution was cooled to 40° C., and 150 g of hydrochloric acid with a concentration of 35 wt % and 75 g of acetaldehyde were added thereto. The liquid temperature was maintained at 40° C. to carry out an acetalization reaction, and the reaction product was precipitated.
Thereafter, the liquid temperature was maintained at 40° C. for 3 hours to complete the reaction, and the mixture was neutralized, washed with water and dried in a conventional manner to obtain a polyvinyl acetoacetal resin powder.
The resulting polyvinyl acetoacetal resin was dissolved in DMSO-D ₆ (dimethyl sulfoxide) and measured by ¹³ C-NMR (nuclear magnetic resonance spectroscopy), which showed that it contained 25 mol % of hydroxyl groups, 74 mol % of acetoacetal groups, and 1 mol % of acetyl groups.

The obtained polyvinyl acetoacetal resin was used as the thermoplastic resin, and an adhesive was prepared by adding the thermoplastic resin, reactive diluent (A), reactive diluent (B) and photoreaction initiator as shown in Table 1.

(Comparative Examples 1 to 3 and 6)
As shown in Table 2, reactive diluent (A), reactive diluent (B) and a photoinitiator were added to prepare an adhesive.

(Comparative Example 4)
An adhesive was prepared from the polyvinyl butyral resin obtained in Reference Example 1.

(Comparative Example 5)
An adhesive was prepared from the polyvinyl acetoacetal resin obtained in Example 8.

(Comparative Examples 7 and 8)
The polyvinyl butyral resin obtained in Reference Example 1 was used as the thermoplastic resin, and the thermoplastic resin, reactive diluent (B), and photoreaction initiator were added as shown in Table 2 to prepare an adhesive.

(Comparative Example 9)
The polyvinyl acetoacetal resin obtained in Example 8 was used as the thermoplastic resin, and the thermoplastic resin, reactive diluent (B), and photoreaction initiator were added as shown in Table 2 to prepare an adhesive.

<Evaluation>
The adhesives obtained in the Examples , Reference Examples , and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

(Measurement of Elastic Modulus and Tan δ Peak Temperature)
The adhesives obtained in Reference Examples 1 to 7, 10, Examples 8 to 9, 11 to 13, and Comparative Examples 1, 2, 4, 5, and 7 to 9 were irradiated with ultraviolet light using a metal halide UV lamp at an irradiation dose of 3000 mJ/ ^cm2 to obtain cured products.
The dynamic viscoelasticity spectrum of the obtained cured product was measured in the temperature range of -50 to 100°C using a dynamic viscoelasticity measuring device DVA-200 (manufactured by IT Measurement & Control Co., Ltd.) with a sample length of 30 mm, a chuck spacing of 20 mm, a frequency of 1 Hz, and a heating rate of 5°C/min, and the elastic modulus at 50°C and the tan δ peak temperature derived from the thermoplastic resin were confirmed.

(Evaluation of Adhesion after Temporary Adhesion)
The adherends used were a PET film (Toyobo Co., Ltd., COSMOSHINE A-4100, thickness 100 μm, the untreated side, not the easy-adhesion treated side, was used as the evaluation surface), a polarizing plate (Nitto Denko Corporation, SEG1425DU), glass (Nippon Test Panel Co., Ltd.), and a prism sheet (Suntech Opt Co., Ltd., 48 μm prism pitch, thickness 45 μm).
The adhesive obtained in each of the Examples , Reference Examples, and Comparative Examples was applied to a PET film to a thickness of 20 μm using a bar coater, and a release-treated PET sheet was laminated thereon to obtain a laminate. The laminate was then irradiated with ultraviolet light at an irradiation dose of 60 mJ/ ^cm2 using a metal halide UV lamp, and the PET sheet was peeled off to obtain a PET film with an adhesive layer.
The adherend was placed on the adhesive layer side of the adhesive-layered PET film, and pressed back and forth once using a 2 kg roller. Note that, for the prism sheet, pressing was performed only in the forward direction using a 30 g roller.
Thereafter, ultraviolet light was irradiated at an irradiation dose of 3000 mJ/cm ² using a metal halide UV lamp to obtain a two-stage cured sample.
The obtained samples were subjected to a 90 degree peel test at a tensile speed of 300 mm/min using a tensile tester to measure adhesive strength, and the adhesiveness after temporary adhesion was evaluated according to the following criteria.

<PET-PET>
⊚: The adhesive strength was 14 N or more.
A: The adhesive strength was 11 N or more and less than 14 N.
Δ: The adhesive strength was 8N or more and less than 11N.
×: The adhesive strength was less than 8N.
<PET-polarizing plate>
⊚: The adhesive strength was 10 N or more.
A: The adhesive strength was 8N or more and less than 10N.
Δ: The adhesive strength was 6N or more and less than 8N.
×: The adhesive strength was less than 6N.
<PET-glass>
⊚: The adhesive strength was 10 N or more.
A: The adhesive strength was 8N or more and less than 10N.
Δ: The adhesive strength was 4N or more and less than 8N.
×: The adhesive strength was less than 4N.
<PET-prism sheet>
⊚: The adhesive strength was 1N or more.
A: The adhesive strength was 0.7 N or more and less than 1 N.
Δ: The adhesive strength was 0.5N or more and less than 0.7N.
×: The adhesive strength was less than 0.5 N.

(Adhesion Evaluation)
The adherends used were the same as those used in (evaluation of adhesion after temporary attachment).
For the PET film, polarizing plate, and prism sheet, the adhesive obtained in the Examples , Reference Examples, and Comparative Examples was applied to the PET film to a thickness of 20 μm using a bar coater, and the adherend was laminated so that the adhesive was sandwiched between the PET film and the adherend to produce a laminate. The resulting laminate was irradiated with ultraviolet light using a metal halide UV lamp at an irradiation dose of 3000 mJ/ ^cm2 , and then cut into a size of 25 mm x 150 mm to obtain a sample.
For glass, the adhesive obtained was applied to a 50 mm x 150 mm glass plate using a bar coater to a thickness of 20 μm, and a PET film cut to 25 mm x 150 mm was placed on top of the adhesive, and pressed using a 30 g roller to produce a laminate. The laminate obtained was irradiated with ultraviolet light using a metal halide UV lamp at an irradiation dose of 3000 mJ/ ^cm2 to obtain a sample.
The obtained samples were subjected to a 90 degree peel test at a tensile speed of 300 mm/min using a tensile tester to measure adhesive strength, and the adhesiveness was evaluated according to the following criteria.

<PET-PET>
⊚: The adhesive strength was 12 N or more.
A: The adhesive strength was 8N or more and less than 12N.
Δ: The adhesive strength was 6N or more and less than 8N.
×: The adhesive strength was less than 6N.
<PET-polarizing plate>
⊚: The adhesive strength was 7N or more.
A: The adhesive strength was 5N or more and less than 7N.
Δ: The adhesive strength was 3N or more and less than 5N.
×: The adhesive strength was less than 3N.
<PET-glass>
⊚: The adhesive strength was 12 N or more.
A: The adhesive strength was 9N or more and less than 12N.
Δ: The adhesive strength was 6N or more and less than 9N.
×: The adhesive strength was less than 6N.
<PET-prism sheet>
⊚: The adhesive strength was 1.4 N or more.
A: The adhesive strength was 0.9 N or more and less than 1.4 N.
Δ: The adhesive strength was 0.7N or more and less than 0.9N.
×: The adhesive strength was less than 0.7 N.

(Luminance Degradation Evaluation)
The PET film and the prism sheet that were not laminated were placed on top of each other on a MUTOH light board, and placed at the center of the light source. A TOPCON BM-9 luminance meter was used to measure the luminance before lamination, with the distance between the light source and the luminance meter set to 350 mm and the luminance meter aligned with the center of the light source. After that, the luminance was similarly measured for the sample using the prism sheet obtained in (Adhesion evaluation).
The luminance deterioration was calculated by the following formula and evaluated according to the following criteria.
(Brightness Deterioration)=(Brightness before bonding−Brightness of sample)/(Brightness before bonding)×100(%)
A: The luminance deterioration was less than 10%.
A: Luminance degradation was 10% or more and less than 12%.
Δ: Luminance degradation was 12% or more and less than 16%.
x: The luminance degradation was 16% or more.

(Haze rating)
Each of the adhesives obtained in the Examples , Reference Examples and Comparative Examples was applied using a dispenser onto a piece of glass measuring 10 cm x 7.0 cm and 1 mm in thickness so that the thickness after application was 100 μm, and the other surface was attached to a piece of glass measuring 10 cm x 7.0 cm and 1 mm in thickness to obtain a glass/adhesive/glass construct (glass-glass construct).

The haze value of the obtained structure was measured in accordance with JIS K 5600 using a color haze meter (manufactured by Murakami Color Research Laboratory).
A: The haze was less than 0.5%.
A: The haze was 0.5% or more and less than 1%.
Δ: Haze was 1% or more and less than 2%.
×: Haze was 2% or more.

According to the present invention, it is possible to provide an adhesive that exhibits surface tackiness to improve temporary adhesion, and furthermore, that is capable of exhibiting excellent adhesive strength even after temporary adhesion due to enhanced adhesion, has excellent transparency, and is capable of suppressing brightness degradation, particularly when used to bond optical films.

Claims (9)

Contains a thermoplastic resin, a reactive diluent (A) and a photoinitiator,
the thermoplastic resin is a polyvinyl acetal resin,
The reactive diluent (A) has a 90 degree peel adhesion strength of 5.5 N/25 mm or more when used to bond PET sheets together, as measured in accordance with JIS K 6851-1:1999;
The adhesive is characterized in that the reactive diluent (A) contains 5 to 85% by weight of a (meth)acrylic acid ester having a cyclic ether structure and 5 to 30% by weight of an epoxy compound . The adhesive according to claim 1, further comprising a reactive diluent (B) other than the reactive diluent (A). The adhesive according to claim 1 or 2, characterized in that the thermoplastic resin content is 5 to 40% by weight. The adhesive according to claim 1, 2 or 3, characterized in that the content of reactive diluent (A) is 30 to 85% by weight. The adhesive according to claim 1, 2, 3 or 4, characterized in that the reactive diluent (A) contains an epoxy compound. 6. The adhesive according to claim 1, 2, 3, 4 or 5, wherein the polyvinyl acetal resin is a polyvinyl acetoacetal resin. The adhesive according to claim 6, characterized in that the cured product cured by irradiation with active energy rays at a dose of 3,000 mJ/cm has a modulus of elasticity of 1 x 105 Pa or more in dynamic viscoelasticity measurement, and a tan δ peak temperature derived from the thermoplastic resin of 60 °C or more. 8. The adhesive according to claim 1, 2, 3, 4, 5 , 6 or 7 , which is used for bonding plastics. 9. The adhesive according to claim 1, 2, 3, 4, 5, 6 , 7 or 8, which is used for bonding optical films.